(1) Field of the Invention
The present invention relates to semiconductor devices and particularly to a semiconductor device including a heterojunction bipolar transistor and a field-effect transistor.
(2) Description of the Related Art
Currently, an InGaP/GaAs heterojunction bipolar transistor to (HBT), which includes an emitter layer made of InGaP having a wide bandgap, is in practical use as a radio-frequency element in an apparatus such as a mobile phone. Recent years have seen much focus given to a Bi-FET, in which a power amplifier including the HBT is controlled using a switching element including a field-effect transistor (FET) integrated on a substrate together with the HBT, and thus there has been an advance in the development of the Bi-FET.
In a general device structure of the Bi-FET, for example, first an FET is disposed on a substrate, and then an HBT on the FET, as shown in US 2005/0184310 (Patent Reference 1). In other words, semiconductor layers in which an FET is disposed are stacked on a substrate, and semiconductor layers in which an HBT is disposed are stacked thereon.